Subject: Re: [PATCH 1/6] run-command API: replace run_processes_parallel_tr2() with opts struct

From: Emily Shaffer <[email-masked]>
Date: Thu, 28 Apr 2022 16:16:42 -0700

On Thu, Apr 21, 2022 at 02:25:26PM +0200, Ævar Arnfjörð Bjarmason wrote:
> 
> Add a new "struct run_process_parallel_opts" to cover the trace2
> use-case added in ee4512ed481 (trace2: create new combined trace
> facility, 2019-02-22). A subsequent commit will add more options, and
> having a proliferation of new functions or extra parameters would
> result in needless churn.
> 
> It makes for a smaller change to make run_processes_parallel() and
> run_processes_parallel_tr2() wrapper functions for the new "static"
> run_processes_parallel_1(), which contains the main logic. We pass
> down "opts" to the *_1() function even though it isn't used there
> yet (only in the *_tr2() function), a subsequent commit will make more
> use of it.
> 
> Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
> ---
>  builtin/fetch.c             | 15 ++++++++------
>  builtin/submodule--helper.c | 12 +++++++----
>  hook.c                      | 13 ++++++------
>  run-command.c               | 40 +++++++++++++++++++++++++++----------
>  run-command.h               | 26 ++++++++++++++++--------
>  submodule.c                 | 13 ++++++------
>  t/helper/test-run-command.c | 13 ++++++------
>  7 files changed, 84 insertions(+), 48 deletions(-)
> 
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index e3791f09ed5..9bc99183191 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -1948,14 +1948,17 @@ static int fetch_multiple(struct string_list *list, int max_children)
>  
>  	if (max_children != 1 && list->nr != 1) {
>  		struct parallel_fetch_state state = { argv.v, list, 0, 0 };
> +		struct run_process_parallel_opts run_opts = {
> +			.tr2_category = "fetch",
> +			.tr2_label = "parallel/fetch",
> +		};
>  
>  		strvec_push(&argv, "--end-of-options");
> -		result = run_processes_parallel_tr2(max_children,
> -						    &fetch_next_remote,
> -						    &fetch_failed_to_start,
> -						    &fetch_finished,
> -						    &state,
> -						    "fetch", "parallel/fetch");
> +		result = run_processes_parallel(max_children,
> +						&fetch_next_remote,
> +						&fetch_failed_to_start,
> +						&fetch_finished, &state,
> +						&run_opts);
>  
>  		if (!result)
>  			result = state.result;
> diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
> index 2c87ef9364f..c3d1aace546 100644
> --- a/builtin/submodule--helper.c
> +++ b/builtin/submodule--helper.c
> @@ -2652,12 +2652,16 @@ static int update_submodules(struct update_data *update_data)
>  {
>  	int i, res = 0;
>  	struct submodule_update_clone suc = SUBMODULE_UPDATE_CLONE_INIT;
> +	struct run_process_parallel_opts run_opts = {
> +		.tr2_category = "submodule",
> +		.tr2_label = "parallel/update",
> +	};

Hm, so now it is possible for a callsite to forget to set these, rather
than to grep for "run_processes_parallel" and notice that everybody else
is already calling "run_processes_parallel_tr2". There are not any
callers of 'run_processes_parallel()' except for a test helper today, so
why do we make this seem optional?

If I'm being honest, I'd rather see everything _but_ the trace2 stuff go
into an opts struct, and then see the same entry points we have today
(run_processes_parallel that takes a struct, run_processes_parallel_tr2
that takes a struct and two tr2 string args). Or, I guess, a single
run_processes_parallel() that only takes a struct, does the right thing
with the trace args, and entirely removes the
run_processes_parallel_tr2 call.

>  
>  	suc.update_data = update_data;
> -	run_processes_parallel_tr2(suc.update_data->max_jobs, update_clone_get_next_task,
> -				   update_clone_start_failure,
> -				   update_clone_task_finished, &suc, "submodule",
> -				   "parallel/update");
> +	run_processes_parallel(suc.update_data->max_jobs,
> +			       update_clone_get_next_task,
> +			       update_clone_start_failure,
> +			       update_clone_task_finished, &suc, &run_opts);
>  
>  	/*
>  	 * We saved the output and put it out all at once now.
> diff --git a/hook.c b/hook.c
> index 1d51be3b77a..eadb2d58a7b 100644
> --- a/hook.c
> +++ b/hook.c
> @@ -123,6 +123,10 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
>  	const char *const hook_path = find_hook(hook_name);
>  	int jobs = 1;
>  	int ret = 0;
> +	struct run_process_parallel_opts run_opts = {
> +		.tr2_category = "hook",
> +		.tr2_label = hook_name,
> +	};
>  
>  	if (!options)
>  		BUG("a struct run_hooks_opt must be provided to run_hooks");
> @@ -144,13 +148,8 @@ int run_hooks_opt(const char *hook_name, struct run_hooks_opt *options)
>  		cb_data.hook_path = abs_path.buf;
>  	}
>  
> -	run_processes_parallel_tr2(jobs,
> -				   pick_next_hook,
> -				   notify_start_failure,
> -				   notify_hook_finished,
> -				   &cb_data,
> -				   "hook",
> -				   hook_name);
> +	run_processes_parallel(jobs, pick_next_hook, notify_start_failure,
> +			       notify_hook_finished, &cb_data, &run_opts);
>  	ret = cb_data.rc;
>  cleanup:
>  	strbuf_release(&abs_path);
> diff --git a/run-command.c b/run-command.c
> index a8501e38ceb..7b8159aa235 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -1738,11 +1738,11 @@ static int pp_collect_finished(struct parallel_processes *pp)
>  	return result;
>  }
>  
> -int run_processes_parallel(int n,
> -			   get_next_task_fn get_next_task,
> -			   start_failure_fn start_failure,
> -			   task_finished_fn task_finished,
> -			   void *pp_cb)
> +static int run_processes_parallel_1(int n, get_next_task_fn get_next_task,
> +				    start_failure_fn start_failure,
> +				    task_finished_fn task_finished,
> +				    void *pp_cb,
> +				    struct run_process_parallel_opts *opts)
>  {
>  	int i, code;
>  	int output_timeout = 100;
> @@ -1780,24 +1780,42 @@ int run_processes_parallel(int n,
>  	return 0;
>  }
>  
> -int run_processes_parallel_tr2(int n, get_next_task_fn get_next_task,
> -			       start_failure_fn start_failure,
> -			       task_finished_fn task_finished, void *pp_cb,
> -			       const char *tr2_category, const char *tr2_label)
> +static int run_processes_parallel_tr2(int n, get_next_task_fn get_next_task,
> +				      start_failure_fn start_failure,
> +				      task_finished_fn task_finished,
> +				      void *pp_cb,
> +				      struct run_process_parallel_opts *opts)
>  {
> +	const char *tr2_category = opts->tr2_category;
> +	const char *tr2_label = opts->tr2_label;
>  	int result;
>  
>  	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d",
>  				   ((n < 1) ? online_cpus() : n));
>  
> -	result = run_processes_parallel(n, get_next_task, start_failure,
> -					task_finished, pp_cb);
> +	result = run_processes_parallel_1(n, get_next_task, start_failure,
> +					  task_finished, pp_cb, opts);
>  
>  	trace2_region_leave(tr2_category, tr2_label, NULL);
>  
>  	return result;
>  }
>  
> +int run_processes_parallel(int n, get_next_task_fn get_next_task,
> +			   start_failure_fn start_failure,
> +			   task_finished_fn task_finished, void *pp_cb,
> +			   struct run_process_parallel_opts *opts)
> +{
> +	if (opts->tr2_category && opts->tr2_label)
> +		return run_processes_parallel_tr2(n, get_next_task,
> +						  start_failure, task_finished,
> +						  pp_cb, opts);
What is the point for this extra layer of indirection? I am confused why
we might not just change the arg list for run_processes_parallel_tr2 and
call it good.

If the final result was to reduce the number of run_processes_parallel.*
functions available I'd be happy to see this change, but as it
introduces even more various entry points into run_processes_parallel.*
I'm not so sure.
> +
> +	return run_processes_parallel_1(n, get_next_task, start_failure,
> +					task_finished, pp_cb, opts);
> +}
> +
> +
>  int run_auto_maintenance(int quiet)
>  {
>  	int enabled;
> diff --git a/run-command.h b/run-command.h
> index 07bed6c31b4..66e7bebd88a 100644
> --- a/run-command.h
> +++ b/run-command.h
> @@ -458,6 +458,19 @@ typedef int (*task_finished_fn)(int result,
>  				void *pp_cb,
>  				void *pp_task_cb);
>  
> +/**
> + * Options to pass to run_processes_parallel(), { 0 }-initialized
> + * means no options. Fields:
> + *
> + * tr2_category & tr2_label: sets the trace2 category and label for
> + * logging. These must either be unset, or both of them must be set.
> + */
> +struct run_process_parallel_opts
> +{
> +	const char *tr2_category;
> +	const char *tr2_label;
> +};
> +
>  /**
>   * Runs up to n processes at the same time. Whenever a process can be
>   * started, the callback get_next_task_fn is called to obtain the data
> @@ -469,15 +482,12 @@ typedef int (*task_finished_fn)(int result,
>   *
>   * start_failure_fn and task_finished_fn can be NULL to omit any
>   * special handling.
> + *
> + * Options are passed via a "struct run_process_parallel_opts".
>   */
> -int run_processes_parallel(int n,
> -			   get_next_task_fn,
> -			   start_failure_fn,
> -			   task_finished_fn,
> -			   void *pp_cb);
> -int run_processes_parallel_tr2(int n, get_next_task_fn, start_failure_fn,
> -			       task_finished_fn, void *pp_cb,
> -			       const char *tr2_category, const char *tr2_label);
> +int run_processes_parallel(int n, get_next_task_fn, start_failure_fn,
> +			   task_finished_fn, void *pp_cb,
> +			   struct run_process_parallel_opts *opts);
>  
>  /**
>   * Convenience function which prepares env_array for a command to be run in a
> diff --git a/submodule.c b/submodule.c
> index 86c8f0f89db..256c6bb4b8f 100644
> --- a/submodule.c
> +++ b/submodule.c
> @@ -1817,6 +1817,10 @@ int fetch_submodules(struct repository *r,
>  {
>  	int i;
>  	struct submodule_parallel_fetch spf = SPF_INIT;
> +	struct run_process_parallel_opts run_opts = {
> +		.tr2_category = "submodule",
> +		.tr2_label = "parallel/fetch",
> +	};
>  
>  	spf.r = r;
>  	spf.command_line_option = command_line_option;
> @@ -1838,12 +1842,9 @@ int fetch_submodules(struct repository *r,
>  
>  	calculate_changed_submodule_paths(r, &spf.changed_submodule_names);
>  	string_list_sort(&spf.changed_submodule_names);
> -	run_processes_parallel_tr2(max_parallel_jobs,
> -				   get_next_submodule,
> -				   fetch_start_failure,
> -				   fetch_finish,
> -				   &spf,
> -				   "submodule", "parallel/fetch");
> +	run_processes_parallel(max_parallel_jobs, get_next_submodule,
> +			       fetch_start_failure, fetch_finish, &spf,
> +			       &run_opts);
>  
>  	if (spf.submodules_with_errors.len > 0)
>  		fprintf(stderr, _("Errors during submodule fetch:\n%s"),
> diff --git a/t/helper/test-run-command.c b/t/helper/test-run-command.c
> index f3b90aa834a..9b21f2f9f83 100644
> --- a/t/helper/test-run-command.c
> +++ b/t/helper/test-run-command.c
> @@ -183,7 +183,7 @@ static int testsuite(int argc, const char **argv)
>  		(uintmax_t)suite.tests.nr, max_jobs);
>  
>  	ret = run_processes_parallel(max_jobs, next_test, test_failed,
> -				     test_finished, &suite);
> +				     test_finished, &suite, NULL);
>  
>  	if (suite.failed.nr > 0) {
>  		ret = 1;
> @@ -371,6 +371,7 @@ int cmd__run_command(int argc, const char **argv)
>  {
>  	struct child_process proc = CHILD_PROCESS_INIT;
>  	int jobs;
> +	struct run_process_parallel_opts opts = { 0 };
>  
>  	if (argc > 1 && !strcmp(argv[1], "testsuite"))
>  		exit(testsuite(argc - 1, argv + 1));
> @@ -413,15 +414,15 @@ int cmd__run_command(int argc, const char **argv)
>  
>  	if (!strcmp(argv[1], "run-command-parallel"))
>  		exit(run_processes_parallel(jobs, parallel_next,
> -					    NULL, NULL, &proc));
> +					    NULL, NULL, &proc, &opts));
>  
>  	if (!strcmp(argv[1], "run-command-abort"))
> -		exit(run_processes_parallel(jobs, parallel_next,
> -					    NULL, task_finished, &proc));
> +		exit(run_processes_parallel(jobs, parallel_next, NULL,
> +					    task_finished, &proc, &opts));
>  
>  	if (!strcmp(argv[1], "run-command-no-jobs"))
> -		exit(run_processes_parallel(jobs, no_job,
> -					    NULL, task_finished, &proc));
> +		exit(run_processes_parallel(jobs, no_job, NULL, task_finished,
> +					    &proc, &opts));
>  
>  	fprintf(stderr, "check usage\n");
>  	return 1;
> -- 
> 2.36.0.893.g80a51c675f6
>